DESCRIPTION: Streptococcus mutans is part of the normal oral flora, and promotes caries under opportunistic conditions. Knowledge of interacting factors between host and S. mutans that contribute to caries is still primitive. Specific Aim 1: Ascertain the influence of specific salivary secretory constituents in the development of caries. We will study three salivary constituents, high molecular weight salivary mucin (Muc19), low molecular weight salivary mucin (Muc10), and salivary amylase (Amy 1). All three genes have been identified in the mouse genome. We will produce knockout mice for direct evaluation in caries experiments. We will also produce double and triple knockout animals to test for additive, synergistic, or possibly even competitive effects on caries. Specific Aim 2: Evaluate S. mutans genes for their role as virulence factors associated with infection of the oral cavity and subsequent caries development. We will focus on: i) glucosyltransferase B/C (gtfB/C) and gtfB/C/D;2) Antigen I/II (Ag I/II);and 3) a putative fibronectin/fibrinogen-binding protein gene that is up-regulated at pH 5 (fbp, Smu. 1449). Ag I/II and fbp will be studied as single mutations, and in the genetic backgrounds, gtfB/C and gtfB/C/D, to help elucidate their roles in the infection process. Binding profiles to hydroxyapatite beads, coated with whole saliva, parotid saliva, submandibular/sublingual saliva, Muc l9, Muc 10 or amylase will be determined. Infectious mutant strains will be tested for induction of caries. We will also perform cDNA microarray analyses of mutant versus wild-type strains to determine whether Fbp functions in the up- or down-regulation of cell-wall associated proteins. We will determine the effects of saliva on gene expression in S. mutans and how the cells respond in the absence of specific genes, gtfs, fbp and AgI/II. Specific Aim 3: Determine the interaction between an S. mutans virulence factor and a specific salivary secretory constituent in the development of caries. As we elucidate the roles of salivary constituents and S. mutans genes in caries, we will then determine contrasting or additive/cooperative interactions between host and bacterial determinates. These studies will delineate specific bacterial and host determinants that function in caries. Future studies can then focus on molecular mechanisms of host-pathogen interactions. Results may indicate important therapeutic targets to treat patients at high risk for caries (i.e., patients with xerostomia).